A single-phase sample of α′ (O′3)-type layered sodium cobalt oxide Na_xCoO₂ (x ∼ 0.78) was prepared and its incommensurately modulated crystal structure was analyzed using the (3+1)-dimensional superspace approach to the powder neutron diffraction data. The crystal structure of the cobaltate is accurately described based on the superspace group C2/m(α0γ)00, wherein the positions of Na atoms are most significantly modulated in the monoclinic a direction to form an ordered arrangement. Such a displacive modulation causes a quasi-periodic shift of Na atoms from the centers of the NaO₆ polyhedra between undulated CoO₂ sheets, changing the form of the NaO₆ polyhedron from an octahedral coordination (O) to a trigonal prismatic (P) one, via an intermediate capped trigonal prismatic NaO₇ coordination (C). At the positions where the Na atoms are most significantly shifted, the neighboring Na atoms are located at almost touching distances. However, the occupation factor of Na atoms becomes zero at such positions, yielding Na-deficient sites V_Na, sandwiched either between C and P, or C and C-type polyhedra.

中文翻译：

---

α' (O'3) 型氧化钴钠 NaxCoO2 (x ∼ 0.78) 的非相称调制晶体结构

制备了 α' (O'3) 型层状氧化钴钠 Na _x CoO ₂ ( x ∼ 0.78)的单相样品，并使用 (3+1) 维超空间方法分析了其不相称调制的晶体结构粉末中子衍射数据。基于超空间群C 2/ m (α0γ)00准确描述了钴酸盐的晶体结构，其中Na原子的位置在单斜a方向上受到最显着的调制，形成有序排列。这种位移调制导致 Na 原子从波状 CoO ₂之间的 NaO ₆多面体中心发生准周期位移。片，将 NaO ₆多面体的形式从八面体配位 (O) 更改为三角棱柱 (P)，通过中间加盖的三角棱柱 NaO ₇配位 (C)。在 Na 原子移动最显着的位置，相邻的 Na 原子位于几乎接触的距离处。然而，在这些位置，Na 原子的占据因子变为零，产生缺_Na位点V _Na，夹在 C 和 P 之间，或 C 和 C 型多面体之间。